1. Field of the Invention
The present invention concerns devices used for debarking tree-trunks.
2. Description of the Prior Art
Tree-trunks are debarked industrially by machines as described in document CA 2 078 355 A, for example, including tree-trunk support means for carrying a treetrunk on its side, moving it in longitudinal translation and rotating it about its longitudinal axis. Debarking knives having at least one debarking edge are pressed laterally against the lateral face of the tree-trunk at a fixed longitudinal position and with an appropriate orientation so that the debarking edge scrapes the bark from the trunk.
Machines of this kind require constant surveillance, in particular because of the wear of the debarking edge of the knives.
This wear progressively blunts the debarking edge and reduces its effectiveness. As a result the bark is incompletely removed, so reducing the quality of the wood for its subsequent use, for example in the manufacture of paper pulp.
It is therefore necessary to change the knives regularly, to renew the debarking edges of the machine.
Plates of a harder material or plates that have received a chemical vapor deposition (CVD) surface treatment, as described in document EP 0 319 926 A, by pressure phase deposition (PVD), by laser nitriding as described in document DE 38 08 285 A, by ionic nitriding, by blown plasma hard metal surface coating, or by high velocity oxidation (HVOF) have been used to increase the service life of certain tools for machining metals. These techniques have not been applied to knives for debarking tree-trunks and are not directly applicable to the particular geometry of debarking knives having a sharp edge.
The problem to which the present invention is addressed is that of conceiving a new debarking knife structure and a method for manufacturing it very substantially increasing the resistance to wear of the debarking edges and retaining the cutting qualities necessary for optimal operation of the debarking machine.
The basic idea of the invention consists in providing a composite structure for the debarking knife which, in use, is subject to progressive wear such that the appropriate geometry of the debarking edge is substantially conserved, whilst reducing the rate of wear of the debarking edge.